As known, the use of conductor bundles for high-voltage electric lines determines the need to dispose spacing elements--at regular intervals along the line--between the elementary conductors of a same bundle, so as to prevent said bundles from intersecting, or at least from overlapping.
Such a drawback may be determined by relative movements of one conductor with respect to the other--deriving from different elongations, from the action of the wind, from breaking loose of ice or snow muffs, or from the external mechanical forces--as well as by electrodynamic effect of mutual attraction, deriving from the short circuit currents whicy may occur on the line.
Spacers designed to connect the sub-conductors of a same bundle should hence satisfy two opposite requirements: on one hand, they must be sufficiently flexible, so as not to damage the conductors at the connection point when they are subjected to normal stresses; on the other hand, they must be sufficiently stout in order to withstand, without undergoing permanent deformation, the compressive stresses deriving from the electrodynamic effect of short circuit currents.
Several types of spacers, capable of performing this double function, are already known. Among these, there is, for example, the spacer described in Italian Pat. No. 834,619.
An important improvement of such spacers has been realized with the so-called "damping spacers", for instance of the type described in U.S. Pat. No. 3,582,983. This patent actually illustrates a structure which--as well as performing the described function of keeping the sub-conductors of the bundle separated and spaced, with a differentiated behavior according to the stresses to which the conductors are subjected--is able to perform a function of dampening the oscillations produced on said conductors by the action of the wind.
The spacer described in this patent has a deformable elastic structure, anchored to the conductors of the bundle through connecting clamps, wherein said clamps comprise rigid extensions, the free ends of which are associated to a stuff central body through at least one springing hinge element. Each hinge element has structural characteristics such as to dissipate energy when subjected to oscillations, in order to accomplish the desired dampening of said oscillations.
In the cited U.S. Pat. No. 3,582,983, each hinge element simply consists of a short length of wire rope, the ends of which are firmly fixed onto the rigid parts which it has to connect. The oscillation energy is dissipated due to the sliding friction between the single strands of the wire rope length.
Other types of damping spacers are described in U.S. Pat. Nos. 3,748,370 and 3,784,723; these in turn comprise a central stiff body, to which the rigid extensions of the connecting clamps are connected by way of springing hinges. Said hinges consist of a pair of mutually rotating elements, between which are interposed rubber pads, which get compressed on rotation--even to a slight extent--of one element with respect to the other, due to oscillation of the clamps with respect to the stiff central body.
Also, the damping spacer described in the Italian patent application No. 22559 A/82, in the name of the same Applicant--the description of which should be referred to for further details of the heretofore specified known technique--comprises springing hinges, incorporating rubber elements. In this structure, however, the rubber elements are not subjected to compressive stresses, but rather to shearing stresses.
In the first as well as in the second case, to the elastic deformation of the rubber elements--produced by the oscillations to which the hinges are subjected--there is associated a dissipation of energy, deriving from the mechanical hysteresis of said rubber elements, and to this dissipation of energy corresponds the desired damping of the oscillations.
All such known devices, though considered fairly efficient for the normal uses foreseen, have however evidenced--in the course of accurate tests--a very low damping force in the event of the bundle of conductors being subjected to low frequency oscillation movements and/or to torsional oscillation movements. In fact, in these cases--and particularly when a so-called "twin-wire" bundle is involved--the stiff central body of the spacer tends to follow the low frequency oscillation or the torsion of the bundle, determining only slightest deformations in correspondence of the hinges and thus very low dampening effect.